Interpretive Summary: There are probably tens of thousands of fungal metabolites, however, the foodborne-fungal metabolites that are suspected or known to cause disease in humans or animals number in the hundreds. For this review, mycotoxins are defined as those that when consumed or absorbed by animals cause sickness or behavioral changes. This definition distinguishes between “fungal metabolites”, “toxic fungal metabolites”, and “mycotoxins”. The number of known mycotoxins that pose a measurable health risk to farm animals is quite limited because, while many fungal metabolites have the potential for toxicity, only a relative few are documented and confirmed to cause toxic effects in field situations. Nonetheless, the knowledge derived from studies with laboratory animals and in vitro studies serve as a warning for the possible contribution of mycotoxins in altering immune function, contributing to unexplained animal diseases, and performance problems in farm animals. Several excellent reviews document the toxicology of mycotoxins in farm animals with extensive descriptions of the clinical manifestations. This review describes the main clinical signs in farm animals exposed to levels of mycotoxins encountered in field outbreaks, metabolism, mechanisms of action and biochemical markers of exposure. The purpose of the review is to highlight those observations that could help to identify the responsible mycotoxin when it is known that the outbreak is a result of consumption of moldy feed. Some clinical signs are unique and some are highly suggestive of a particular mycotoxin. While it would be most useful to have simple mechanism-based biochemical markers that provide definitive identification of a specific mycotoxicosis, this is only possible for a very few mycotoxins. Thus, from a forensic perspective, the investigator must use all the tools available to identify the cause of a feedborne disease outbreak.